1. Field of the Invention
The invention relates to a fluid displacement apparatus with a suction valve mechanism and, more particularly, to a valved suction mechanism of a piston-type refrigerant compressor used in an automotive air conditioning system.
2. Description of the Related Art
Piston-type compressors, such as a swash plate-type compressor and a wobble plate-type compressor, are known in the art. For example, U.S. Pat. No. 4,976,284 to Hovarter describes an air conditioning device used for a vehicle employing a multi-cylinder, piston-type compressor with reciprocatory piston, and a suction and discharge valve mechanism. The suction and discharge valve mechanism has a valve plate defining suction and discharge ports and a valve sheet defining resilient reed valves therein. The ends of a cylinder block are closed by front and rear housings, through the valve plate, so that suction and discharge chambers are formed in each of the housings.
The suction chamber is in fluid communication with the compression chambers through a suction valve mechanism having suction ports, which are formed in the valve plate, and suction valves, which are arranged on the inner side of the valve plate. Discharge chambers are in fluid communication with the compression chambers through a discharge valve mechanism. The discharge valve mechanism includes discharge ports, which are formed in the valve plate, and discharge valves, which are arranged on the outer side of the valve plate. The housing is provided with inlet ports, which permit refrigerant gas to be introduced from the eternal portions of the air conditioning circuit and to flow into the suction chambers, and outlet ports, which permit a compressed refrigerant gas to flow from the discharge chambers into the air conditioning circuit. A free end of each suction valve is resiliently bent and moves away from the valve plate due to the differential between pressure within the compression chambers and that within the suction chamber during the suction stroke of the reciprocating piston in the compression chamber.
When the discharge stroke ends and the subsequent suction stroke begins, each suction valve is bent to an open position by the differential between a reduced pressure within the compression chamber and the pressure prevailing in the suction chamber of the housing. The suction port is opened to allow the refrigerant gas in the suction chamber to be drawn into the compression chamber. When the suction stroke ends and the compression stroke begins, each suction valve returns to the closed position, to close the suction port under the high pressure of the compressed refrigerant gas, and the associated discharge valve is moved to the open position, to open the discharge ports by the high pressure of the compression gas.
In the above described construction and operation of a known suction valve mechanism of the reciprocating piston-type compressor, the cross-sectional area of each suction port is designed to be constant. Therefore, starting torque shock may to occur at the time of starting of the compressor because a relatively large amount of refrigerant gas is introduced into the compression chamber and a great deal of power is required to compress the refrigerant gas.
In an attempt to solve this problem, the cross-sectional area of each suction port is designed to be significantly reduced. However, during the operation of the compressor, the discharge ability of the compressor is reduced due to the pressure loss of the refrigerant gas through small suction ports. Therefore, it is difficult to simultaneously resolve each of the above-mentioned problems.